Shoes with improved comfort are sought after by consumers and is a goal of shoe suppliers. Comfort is provided in three basic ways, materials of manufacture, shoe shape and cushioning. In addition to comfort, shoes worn at work sites are constructed to provide an extra margin of safety such as superior slip resistance. Slip resistance is an important feature in certain work sites such as restaurants where liquids are frequently on the floors in areas where workers walk and stand. In addition to these functional features, style can also be important particularly in areas where the public visits.
Cushioning can be provided by the insole, midsole and outsole with suitable materials of construction. Although soft soles provide comfort, they tend to be very flexible. Many of these components are made of a cellular or foam material. In addition, air cushions have been used in the heel area of the shoe particularly to reduce impact forces. The cushioning is used to reduce impact on the shoe user during use of the shoe, particularly during fast walking and running where the heel of the user first impacts the underlying surface. One problem with air cushions is that movement of entrapped air inside the cushion in one area causes other areas of the cushion to accommodate that movement, e.g., if one area is compressed, another area expands in a flexible fluid filled cushion.
Shoes that have a rounded bottom have been found to enhance safety by maintaining the shoe in contact with the ground throughout the step. For this reason the round shape has even been used for supporting of a cast used while a foot is being rehabilitated. For instance, U.S. Pat. No. 2,278,626 is a cast support having a rounded bottom, the shape maintaining the healing foot in constant contact with the ground throughout the step. In addition, the shape has a fairly narrow bottom that causes the muscles to work during the walking step by requiring muscle rehabilitation.
U.S. Pat. No. 3,566,487 discloses a cast shoe which is thicker at the center than at the heel and toe to form a curved rocker-like lower surface. A thick resilient sole covers the lower surface, and a soft flexible upper covers the arch. The inner surface of the shoe carries a layer of resilient flexible material.
U.S. Pat. No. 3,835,556 discloses a shoe base having a rigid platform wherein the ground-contacting surface of the platform extends in a continuous convex curve from the front-end to the rear-end of the platform. The convex curve includes a middle portion for location beneath the foot arch of the wearer which has a radius of curvature greater than the portions of the convex curve laying either side of the middle portion.
U.S. Pat. No. 4,372,059 discloses a shoe sole having a resiliently deformable middle segment which provides resilient, cushioned support for the arch of the wearer's foot and distributes the wearer's weight on the feet while standing, walking or running. The arch-supporting middle segment of the sole is resiliently deformable so that it pushes up against the arch of the wearer's foot when its normally convex bottom face is flattened while the wearer is standing still, and also during each step while walking or running until the foot is pivoted forward to put most of the wearer's weight on the toes and the ball of that foot. The entire shoe sole is a one-piece molded body of resiliently deformable material which is more readily deformable in the arch-supporting middle segment than in the heel-supporting rear segment and the toe-supporting front segment.
U.S. Pat. No. 4,241,523 discloses a shoe rocker member which is longitudinally curved to form a load-bearing pedestal aced beneath the base. One end of the rocker member is pivotally secured to the base and the other end is spaced from it. The space between the rocker member and the base is filled with resilient material.
U.S. Pat. No. 4,262,433 discloses a shoe having a central rocker portion formed on the bottom of the sole body substantially midway between the front end and the rear end of the sole body and connecting with said front groove with a heel formed on the rear part of the sole body. The rocker portion is arcuate convexly outwardly of the sole body on an axis perpendicular to the longitudinal axis of the sole body and extending outwardly beyond a plane connecting the outermost surface of said fore part portion and said heel whereby a roll action of the sole body is provided between the initial contact of the compressible heel and the fore part in the gait of the user.
U.S. Pat. No. 5,579,591 discloses a shoe having an upper and a sole, and a heel region having a thickness from a sole upper surface to the ground. The thickness is formed thinner at a backward portion than at a forward portion, whereby a line connecting a position on a lower surface of the sole under the head of the second metatarsus to a front end on a lower surface of the heel region of the sole is lifted at an angle with a horizontal line connecting a grounded rear end on the lower surface of the heel region to a front end thereof in a state where a weight is loaded to a human heel, and the backward portion of the heel region comprises an impact absorbing mechanism, whereby a level of the heel portion which is in contact with a foot is depressed when loaded.
U.S. Pat. No. 2,001,821 discloses the use sponge rubber, rubber coated fiber, and elastic compositions for cushioning of the foot when used in footwear.
U.S. Pat. No. 4,236,326 discloses a shoe have an upper bonded to a sole by adhesives. The shoe sole comprises a ground sole, an interlayer sole bonded at its upper surface to the shoe upper and bonded at the toe of its lower surface to the above ground sole, and an interlayer body situated at the heel portion. The shoe sole is made of rubbery material in which the ground sole at the lowermost layer consists of rigid rubber or polyurethane, and the interlayer sole and the interlayer body consists of soft rubber, polyurethane, sponge and the like.
U.S. Pat. No. 6,782,639 discloses a rounded bottom shaped shoe with a disclosure directing the shoe for use in dynamic, rolling walking action. The shoe has an upper part provided with an upper, a midsole, a midsole bottom, an undersole and a sole bottom. The sole bottom has a curved shape when unloaded that is substantially continuous and convex, without any abrupt changes in radius of curvature, along substantially the entire length thereof and includes a hard, wedge-shaped inclusion. The hard inclusions can have a random shape and size. The hard inclusions makes it possible to precorrect incorrect or abnormal postures of feet, such as in the case of skew or flat feet or abnormal postures of the knee or hip position, as well as spinal column postural deficiencies. The hard inclusions also permit massaging effects, the stimulation of foot zone reflexes and the planning of coordinated movements.
Patent Application 2008/0229624 discloses a diagonally twisted sole by inclusion of a twisted plate built into the sole.
There is thus a need for an improved shoe construction to overcome the problems attendant with the use of rounded bottoms.